There exists a need for a low cost method to enhance the quality of paper and paper board made from southern pine or fiber from other softwood species. The over use of hardwood in the production of paper products, especially in this country, has reduced the quantity of available hardwoods and consequently driven up the price of these woods as raw materials. Therefore, not only is the need for a process that employs softwoods, instead of hardwoods, economically driven, it is also environmentally driven. The problem with paper product produced from softwood is that it yields a rough finished product with low quality surface features.
The prior art, particularly, Canadian Patent No. 2,060,105 teaches the use of microcrystalline cellulose (hereinafter “MCC”) addition to paper products. The MCC used in the prior art processes, however, is of the commercial high grade variety. Commercial MCC is generally defined as having a 97% cellulose content (US Pharmacopoeia USP 23 NF 18). This high degree of cellulose concentration is achieved through various techniques known in the art such as hydrolysis, enzymatic action, pressurization, reactive extrusion and combinations of the above. See U.S. Pat. Nos. 2,978,446; 6,228,213; 5,543,511 and 4,427,778. All of these processes, however, render the final paper product uneconomical. Moreover, none of these patents teach the hydrolysis of a low grade pulp to produce texturized microcrystalline cellulose with a cellulose content of 90% to be used for surface treatment of paper and paper board. Additionally, many of these techniques require processing equipment that is not traditionally employed at paper production facilities, especially the processes that require enzymatic action.
MCC has traditionally been difficult to develop in a cost effective manner for usefulness in surface treatment of paper. The market value of MCC powder is known to range from $5,000 to $10,000 per ton. CELLULON®, manufactured by Weyerhaeuser, for use as a surface treatment for paper, is a biologically produced cellulose microfibril material that costs roughly $6 to $10 per pound, thereby rendering it prohibitively expensive (see D. C. Johnson, A. R. Winslow, “Bacterial cellulose has potential application as new paper coating”, Pulp & Paper, May 1990, page 105–107). Therefore, the need exists for a low cost MCC in micron sizes that can be used to increase the quality of low grade paper or paper board, especially that made from softwoods.
Further, commercial quality MCC, if texturized and transformed into suspension of particles of 5–30 microns, generally has a viscosity in the range of 20,000–200,000 cPs. Surprisingly, lower viscosity MCC produced by the present process also is more effective as a surface treatment for paper and paper board due to the nature of paper fibers and the filling nature of a low viscosity-submicron material.